Sepsis remains one of the major health threats in the U. S., affecting ~750,000 Americans per year, with mortality rate up to 50%. Many septic patients survive the initial ?cytokine storm? but develop profound immunosuppression, become immunocompromised and succumb to secondary infections. Monocytes from such immunocompromised septic patients have ?re- programmed? Toll-like receptor (TLR) 4 signaling, showing suppressed pro-inflammatory cytokines but unchanged or increased expression of anti-inflammatory and anti-microbial mediators, reminiscent of endotoxin tolerance. Long non-coding RNAs (lncRNAs) have recently emerged as new regulators of TLR signaling pathways, but how changes in lncRNAs ?shape? re- programming of responses of myeloid cells during TLR tolerance and sepsis is unknown. Our preliminary and published data has identified lncRNAs in human THP1 monocytes and mouse macrophages with significant changes in expression upon TLR4 challenge and endotoxin tolerization. We showed that knock-down of PCGEM1 lncRNA in THP-1 cells and deficiencies of natural antisense transcript-IL-1?, linc-Cox2 or Eps lncRNAs in mouse macrophages significantly affect LPS signaling. We also found that Eps-/- M?s are compromised in the induction of endotoxin tolerance. These data supports our hypothesis that altered expression and functions of lncRNAs in myeloid cells promote TLR tolerance and sepsis-associated immunosuppression by reprogramming TLR responses at the level transcriptional and post-transcriptional regulation of inflammatory mediators. To test this hypothesis, we have designed the following Specific Aims: 1. Identify the impact of TLR4 tolerance and sepsis on expression of lncRNAs in myeloid cells; and 2. Determine the functional significance for lncRNAs in TLR4 signaling and tolerance. Having completed this project, we will determine the role for lncRNAs in ?reprogramming? of TLR signaling in myeloid cells during development of TLR tolerance and sepsis. This project is expected to improve our understanding of the mechanisms by which lncRNAs modulate antimicrobial responses of myeloid cells, and define molecular targets of lncRNAs for future translational research in human patients with sepsis. These advances would be of key importance for improving treatment of sepsis in the U.S.